The cervical spine is the neck portion of the spine. The cervical spine has a series of seven vertebrae connecting the skull to the thoracic spine (upper back). These seven vertebrae are referred to as C1-C7, with C1 being closest to the skull and C7 being furthest from the skull. Each pair of neighboring vertebrae forms a cervical spine segment that allows movement of the spine, such as rotation and flexion. Each cervical spine segment includes an intervertebral disc that separates the two vertebrae to allow for smooth joint movement and provide cushioning.
The cervical spine houses the spinal cord responsible for neural communication between the brain and the body. Therefore, damage to the cervical spine can lead to neck pain, apparent pain in other parts of the body, and/or impaired functioning. For example, damage to the cervical spine may result in apparent arm pain or partial/complete loss of hand function. Although cervical spine damage may be caused by trauma, cervical spine damage usually is a gradual process occurring with aging. Common cervical spine damage includes degeneration of the intervertebral disc and degeneration of the uncinate joints located adjacent the intervertebral disc space. Intervertebral disc degeneration may cause spinal cord or nerve impingement from the formation of bone spurs and/or intervertebral disc protrusion. Uncinate joint degeneration may cause spinal cord or nerve impingement from the formation of bone spurs. Surgery may be required to resolve either of these issues.
Surgical methods used to resolve cervical spine damage traditionally include cervical discectomy (removal of intervertebral disc). The purpose of such surgery is to restore proper spacing between the cervical vertebrae of the damage cervical spine segment. The intervertebral disc may be replaced by a cage that includes bone graft material for subsequent fusion of the cervical spine segment. A fused cervical spine segment is stiff and does not allow for joint movement. Alternatively, the intervertebral disc is replaced by an artificial disc device that allows for active joint movement of the cervical spine segment.
Conventionally, cervical discectomy is performed from the front (the anterior side). To access the cervical spine segment, the surgeon (a) makes a skin incision in the front of the neck, (b) makes a tunnel to the spine by moving aside muscles and retracting the trachea, esophagus, and arteries, and (c) lifts and holds aside the longus colli muscles that support the front of the spine. Next, the surgeon screws pins into both the superior (upper) cervical vertebra and the inferior (lower) cervical vertebra of the cervical spine segment and uses these pins to increase the intervertebral spacing. The surgeon then performs the cervical discectomy and inserts a cage into the intervertebral disc space.
When the cage includes bone graft material, bone growth within the intervertebral disc space takes place over the next several months, ultimately fusing the cervical spine segment. Each vertebral body (the portion of the vertebra located above or below the intervertebral disc space) has a denser shell of cortical bone surrounding an inner, cylindrical core of spongy cancellous bone. At the intervertebral disc space, the cortical bone shell forms a ring around the cancellous bone. Fusion of the cervical spine segment requires bone growth between the two cortical bone shells of the cervical spine segment.